Input apparatuses or electronic appliances such as smart mobile devices (Smart Phone), digitizers or tablets or e-books/green books include a plurality of antennas or sensor coils forming a sensing plane arranged under a work surface of the digitizer tablet or a screen of the e-book, and a pointer for a user to operate the input apparatuses or electronic appliances. The coordinates of the pointer are obtained through the transmitting and receiving of electromagnetic waves between the circuit of the pointer and the antennas or the sensor coils.
The circuit of the pointer including electromagnetic pens or styluses usually comprises an inductor, a capacitor and relative components enclosed in a case. The inductor constituted by a ferrite core winded with a metal coil and the capacitor constitute the circuit to transmit and receive electromagnetic waves with the antennas or sensor coils. The frequency variation of the circuit is achieved via changing the capacitance and the inductance so that the design of the pointer can choose either the inductor or capacitor to be variable or adjustable according to the requirement.
Through the variation of contact force of the tip of an electromagnetic pen or a stylus applied upon a digitizer or tablet, the pen core is displaced to moved the ferrite core inside the metal coil as well as related components and to press and deform an elastic material such as rubber to change the inductance, capacitance and frequency of electromagnetic signals. U.S. Pat. Nos. 5,565,632 and 6,853,369 disclose such kind of electromagnetic pen.
U.S. Pat. No. 5,565,632 discloses that the inductance and frequency of the electromagnetic pen are changed through the relative displacement of a small ferrite core ahead a large ferrite core with a winding coil. U.S. Pat. No. 6,853,369 shows an electromagnetic pen design with a sensitive variable capacitor which is able to be changed via the variation of the force of the pen core applied, and the frequency is changed according to the capacitance of the variable capacitor.
The disadvantage of the electromagnetic pen disclosed in U.S. Pat. No. 5,565,632 includes incline angle distortion and coordinate fluctuation of the electromagnetic pen. The problem of incline angle distortion results from the variation of the distribution of magnetic lines when the small ferrite core moves ahead the winding coil. The problem of coordinate fluctuation is induced by the variation of the amplitudes of electromagnetic signals when the small ferrite core moves ahead the winding coil. Moreover, the illustrated design lacks an adjustable structure to adjust possible frequency deviation.
The disadvantage of the electromagnetic pen taught an U.S. Pat. No. 6,853,369 includes inaccurate frequency induced by unavoidable manufacturing tolerances of dimensions (length or height) and lack of a remedial design of adjustable structure.
Furthermore, for most input apparatuses such as digitizer tablets, the size of the pointer, particularly the diameter of the pointer, is not specifically required small and has a similar size with ordinary pens for writing. Instead, the pointer must have a relative larger size than that of the ordinary pens for enclosing necessary circuit and components. However, for electronic appliances such as smart phones, mobile communication devices e-books/green books or other portable electronic devices with a limited thickness which have to accommodate the pointer inside, the size of the pointer, particularly the diameter of the pointer, must be small enough for being accommodated inside the electronic appliance.
In view of the problems of manufacturing techniques and design of the conventional pointer devices, the invention provides an electromagnetic pointer to solve these issues.